As worldwide petroleum deposits decrease, there is rising concern over petroleum shortages and the costs that are associated with the production of carbon-based fuel sources. As a result, alternatives to products that are currently processed from petroleum are being investigated. In this effort, biofuel has been identified as a possible alternative to petroleum-based fuels. In general, a biodiesel is a fuel comprised of mono-alkyl esters of long chain fatty acids derived from plant oils or animal fats. In industrial practice, biodiesel is created when plant oils or animal fats are reacted with an alcohol, such as methanol.
Apart from using animal fats, the creation of biofuels from plant oils has gained wide attention in recent years. The process of creating biofuel from plant oils, of course, necessarily begins by growing and harvesting plants such as algae cells. In particular, algae is known to be one of the most efficient plants for converting solar energy into cell growth, so it is of particular interest as a biofuel source.
In an algae cultivation system, the algae cells are typically grown in a cultivation apparatus as part of a liquid medium that is exposed to sunlight to promote photosynthetic growth. Further, the algae cell growth process normally requires the liquid medium to be continuously circulated through the system to allow algae cells to ingest nutrients. Three of the most prevalent algae cultivation apparatuses in use today which meet these requirements are: (1) a photobioreactor, (2) a cultivation pond with a circulation device, and (3) a cultivation pond without a circulation device. Despite having numerous advantages when growing algae, these apparatuses have significant disadvantages, many of which involve biofouling. With biofouling, algae cells tend to adhere to or accumulate on various surfaces. In particular, the algae cells adhere to a light transmitting cover and to the bottom and walls of the apparatus. Importantly, biofouling can significantly decrease the productivity of an algae cultivation system. In detail, if biofouling occurs because algae cells adhere to the light transmitting cover, photosynthesis is disrupted as less light reaches algae cells. In addition, when algae cells remain stationary on a surface, several problems arise: (1) algae cells may die and provide a food source for contaminants like protozoa; (2) algae cells settled too deep below the surface of the water will not receive enough light; and (3) algae cells will not move enough to ingest nutrients floating in the algal culture. All of these problems cause significant disruptions to an effective algae cultivation system.
Various efforts have been made to continuously circulate algal culture. Yet, biofouling still causes significant problems to algae cultivation systems. For one, system efficiency is hindered as algae cultivation systems must be drained and cleaned often to remove the algae cells that have adhered to various surfaces. These interruptions can be minimized by using a device or method that forcefully removes algae cells from surfaces and also serves as an impetus to circulate algae cells in the system.
In light of the above, it is an object of the present invention to provide a system and method for growing algae for biofuel production which minimizes the effects of biofouling. Another object of the present invention is to provide a system and method for growing algae that uses a pulse flow to increase the efficiency of the system. Yet another object of the present invention is to provide a system and method for growing algae using pulse flow circulation that is simple to implement, easy to use, and comparatively cost effective.